Method of automatically detecting offside in Soccer using fixed and wireless sensors and central server

ABSTRACT

Broadly speaking, the embodiments of the present invention fill the need for a method of accurately determining if an offense soccer player is in an offside position. This is determined using a combination of sensors on the players and the ball which are then sensed using fixed sensors on the field. The instantaneous sensor readings are used to locate each player, offense and defense with respect to the location of the ball and goal posts. These data are analyzed using an algorithm on a computer which can then determine if the player was in an offside position.

BACKGROUND

Soccer¹ (or football outside the USA) is a fairly simple game withsimple rules. In its official FIFA form, 11 players on each side (one ofwhom is a goalkeeper) attempt to put a ball into the opponents goalusing only their feet, chest or head. Only the goalkeeper is allowed touse his hands when the ball is in play. While there are 22 players on afield, they are only 3 referees supervising an area of nearly 100×130yards. This makes ruling on fouls and infraction limited to visualverification of one of the referees. One particularly complicated ruleis the one the decides if an offense player is to be ruled offside. 1http://en.wikipedia.org/wiki/Soccer

Offside² effectively limits how far forward attacking players may bewhen involved in play. This prevent a player from gaining an advantageby waiting for the ball near the opposing goal with only the goalkeeperbetween him and the goal. A player is in an offside position if “he/sheis nearer to his opponents' goal line than both the ball and the secondto last opponent,” unless he is in his own half of the field of play. Aplayer level with the second to last opponent is not in an offsideposition. In addition, a player can stay in a “offside” position so longas he/she is not the first offense player to field the ball. Tocomplicate matters further, if two players of the attacking team onlyhave one defender (typically the goalkeeper) between them and the goal,it is allowed for them to pass the ball between each other, as long asthe player passing the ball is ahead of the player receiving it becausethe ball is nearer to the goal line than the receiver, therefore he/sheis not at an offside position2http://en.wikipedia.org/wiki/Offside_%28football%29

As a consequence, offside one of the most incorrectly called infractionleading to fan discontent and, in extreme cases, violence. Therefore, aneutral, technologically sound solution is needed to accurately decideon this complicated rule.

SUMMARY

Broadly speaking, the embodiments of the present invention fill the needfor a method of automatically detecting if a player is in an offsideposition. The embodiments describe methods that are based on usingwireless sensors on players and the ball. These sensors are read orsensed using fixed detectors at several locations on the field. Thefixed detectors provide and accurate location of all players at anygiven instant and their relative location with respect to the ball. Thetwo teams will have distinct sensors and each player with the team canbe equipped with a individualized sensor. A central computer will becontinually reading the inputs from the fixed detectors and constantlyupdate the position of each individual players and the soccer ball. Aspecialized algorithm will then evaluate for an offside infraction inaccordance with the rules.

It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system, adevice, or a method. One inventive embodiment of the present inventionis described below.

In one embodiment, each player has an individualized wireless sensordistinguishing him/her from the other team as well as ones own teammates and a distinct sensor on the ball. The field has fixed detectorson several locations along the edge. The method includes (1) read insensor signals from the fixed detectors to a central server, and (2) use“triangulation”³, “trilateration”s⁴ or “multilateration”⁵ methods toaccurately detect the location of each player and the ball. The methodalso includes (3) determining if the players are in the opposite half ofthe field. The method further includes (4) determining if the ball is infront of the offense player. If the ball is not in front of the offenseplayer, (5) determine if at least two defenders are in front of theoffense player AND the ball is behind the offense. Further (6) If (5) istrue, check if the offense player stays behind defenders until ball islaunched.3http://en.wikipedia.org/wiki/Triangulation4http://en.wikipedia.org/wiki/Trilateration5http://en.wikipedia.org/wiki/Multilateration

The advantages of the present invention will become apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, andlike reference numerals designate like structural elements.

FIG. 1 shows a representation of a soccer field with the players ofeither side represented by their sensors, the ball sensor and the fixedsensors marking the extent of the field.

FIG. 2 shows an example of how a player's location can be determinedusing a combination of fixed and moving sensors. The location of themobile sensor is determined using time of flight of the signal betweenthe multiple sensors.

FIG. 3 is a flow chart that provides an algorithm flow to detect if aplayer is in an offside position.

FIG. 4 demonstrates the algorithm that uses a players current andprevious positions along with that of the ball to determine offsideinfraction.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention.However, it will be apparent to one skilled in the art that the presentinvention may be practiced without some of these specific details. Inother instances, well known implementation details have not beendescribed in detail in order to avoid unnecessarily obscuring theinvention.

As described earlier, offside rules are determined based on acomplicated set of rules that need visual confirmation of the relativelocations of the ball and offense player with respect to the defense,not only at the instance in question, but also their relative positionsprior to the infraction.

It is impractical and expensive to locate several cameras across thefield recording the game which would then have to be synchronized tostudy the relative positions of all involved players during the periodin question. In addition, the limited vision of each camera wouldneccessitate several closely spaced locations each of which would needthe video information stored to be readily accessed.

Therefore, a simple, yet robust technological solution that causesminimal impact on either the players or the field of play is needed.This solution should not require a large infrastructure demand and theresults should be easily and quickly accessible.

The current invention solves the above problem of determining relativepositions of each of the players and the ball at all times by attachingsmall wireless sensors on to each player and the ball. The sensors areuniquely coded and can be understood as providing the same function asthe individual jersey numbers on the back of each player. In addition,the ball will also have a unique sensor affixed to it, providing a wayof locating its position in the field of play. Finally, the locations ofeach of these mobile sensors are determined using an array of fixedsensors located at predetermined locations on the edge and inside thefield of play.

FIG. 1 shows a snapshot of a soccer field with each player representedby a unique sensor symbol. The offense and defensive players, asdetermined by the location of the ball at that instant can be uniquelyidentified by their sensors tags (“#” and “+”). The soccer ball,identified by the symbol “o” has a unique sensor different from allother sensors and is the only one of its kind on the field at any giventime. In addition, several fixed sensors (“*”) along and on the fieldthat will be used to determine the location of each player and ball isalso shown on the figure.

The fixed sensor locations are predetermined and each one is connectedto a central server or a combination of connected computers that performthe analysis of the data collected by the sensors. The fixed sensors canbe connected to the central computation device using a combination ofwired and wireless methods.

Each fixed sensor can locate the physical location of any mobile sensor,in this case, the ball and any player on the field from either side. Inaddition, the sensors can be designed to provide a unique signalidentifying the half of the field that it is located in. Thedetermination of the half of the field will determine which team is“offense” and which one is “defense”. For example, of the ball is inTeam 1's half, all Team 2 players in that half are considered “offense”and Team 1 players are defense and vice-versa. By definition, no playercan be offside in their own half.

There are several methods that can be used to determine the physicallocation of a moving object in a two-dimensional (2D) orthree-dimensional (3D) system. Common amongst these are triangulation,trilateration and multilateration. FIG. 2 presents an example ofdetermining the location of an unknown object using three fixed sensors.The distance between each of the sensors in a Cartesian 2D plane isknown and fixed for the duration of the exercise. The absolute distanceof the mobile object from the fixed sensors is calculated using time offlight measurements (TOF) which locate the distance using the timeneeded for a signal to complete the round trip to the mobile sensor andback.

Trilateration on a 2 dimensional plane needs three known fixed points(relative to each other) to determine a fourth arbitrary point. Thedistance between the fixed sensors S1, S2 and S3 on FIG. 2 are known andassumed to be fixed at all times. The distance from the mobile sensor,M, to any of the fixed sensors is determined by measuring the time offlight (TOF) from each fixed sensor to the mobile one. The location ofmobile sensor at any given instant can be reduced to a simple set ofsimultaneous equations via a set of Cartesian transformations.

Since each of the distances in FIG. 2 are known at any instance of time,the calculation the location of the mobile sensor into Cartesiancoordinates is relatively simple involving well know translation ofdistances into (x,y) coordinates. This can be programmed into a computerto provide instantaneous (x,y) locations of all relevant objects on thefield of play.

FIG. 3 shows a flow chart of the logic used in determining if a playerwas in an offside position at any given time. This flow chart representsa continuous loop of a computer program used to determine positions ofplayers and the ball during the game. At step 301, the locations of allthe individual mobile sensors are read into the system. Since a mobilesensor can be close to several of the fixed sensors on the field, therewill be several relative distance measurements reported for each mobilesensor. These relative distances are determined by the time of flight;i.e., the time taken for a signal to travel from the fixed sensor to themobile sensor and back. Since the signals used in most of thesetechniques are in the electromagnetic spectrum, the distance can then besimply calculated using the speed of light, which is for purposes ofthis discussion considered a universal constant.

Step 302 involves converting the relative distances of the mobilesensors to a fixed coordinate system. There are several well knowtechniques that are used in locating positions of an unknown objectusing its relative distance from several know fixed objects.Triangulation, trilateration and multilateration are a few of these wellunderstood numerical techniques.

Step 303 of FIG. 3 involves physically locating the ball into one of thetwo halves of play. This step is very important since this uniquelydetermines the status of any player as “offense” and “defense”. If theball is in Team l's half, then all Team 1 players are automaticallyconsidered “defense” and vice-versa. If the ball is being propelled byTeam 2 players in Team 1's half (step 304) then the next step (306) isto determine if all Team 2 players (constituting offense at thisparticular instant) are behind the ball. If this is the case, no furtheranalysis is needed and the algorithm returns back to step 301.

If there is at least one team 2 player in team 1's half between the balland the goal post, then a determination of potential offside infractionhas to be made. Step 307(a and b) of FIG. 3 is in itself a mini looplocating the positions of each of the team 2 players (offense) inpotential offside locations with respect to team 1 players (defense) andthe goal post. For each offense player that is located between the balland the goal post, the algorithm determines if there are at least twodefense players between the offense player and the goal post. If this istrue, then the offense player is not ruled offside.

If at least one offense player is located between the ball and the goalpost with less than two defensive players between them, then the personis tagged as being in an offside position. However, the ruling ofoffside cannot be called unless this particular player interacts withthe ball, if and only if a player in an offside position touches theball will he or she be ruled offside. Therefore, the programimplementation of this algorithm will have to save severalchronologically previous positions for each player to ensure a correctruling.

FIG. 4 elaborates the algorithm used in steps 307 a and 307 b todetermine offside based on current and previous positions. In step 401,an offense player that is currently between the ball and goal isdetermined to check if he/she was previously in offside position.

Step 402 determines if the a player in previously offside positiontouched the ball, if true, an offside infraction is called. If not, theloop goes back to the next player.

If the a player was not previously tagged to be in an offside position,step 403 is followed to determine if the player is currently in anoffside position, if true, the player is tagged to be so and the loopgoes back to the top.

If none of the above offside criterion are met, the algorithm in FIG. 3loops back to step 301 and begins collecting the sensor readings for thenext time step.

1. A method of determining offside in soccer using a combination ofsensors on the players and detectors on the field, all analyzed using acentral server: (1) assign distinct wireless sensors for players, withthe two teams being clearly distinguishable; (2) a third distinct classof sensor on the ball to allow it to clearly distinguished from theothers; (3) A network of fixed detectors along the field which readinputs from the sensors; these detectors can be on the field as well ason the goal posts. (4) determine the location of each player and theball using “triangulation” or other location detection methods, (5)determine if the ball and the offense player is on the opposite side ofthe field, if the ball is not near the offense player, ensure that thereare at least two defense players between the offense player and theopposite goal, (6) determine if the offense player was not offside whenthe ball was passed to him, if the offside criterion are met, enable asignal to indicate the infraction
 2. The method of claim 1, wherein thefixed detectors can be connected to the central server using wirelesstechniques
 3. The method of claim 1, wherein the fixed detectors can beconnected to the central server using wired techniques
 4. The method ofclaim 1, wherein the sensors can be battery powered or self powered. 5.The method of claim 1 wherein the centralized server can be made up ofseveral computation units.
 6. The method of claim 1 wherein the numberof players on the field is less than the standard regulation of elevenper side.
 7. The method in claim 1 where the size of the soccer fielddiffers from regulation standards.
 8. The method in claim 1 where thegame can be played indoors as well as outdoors.
 9. The method in claim 1where the location of the players and the ball is determined usingtriangulation.
 10. The method in claim 1 where the location of theplayers and the ball is determined using Multilateration.
 11. The methodin claim 1 where the computer program saves limited time stampedplayers' physical locations.
 12. The method in claim 1 where thecomputer program saves time stamped players' physical locations for theentire game.
 13. The method in game 1 where the stored information canbe used for post-game analysis and learning.
 14. The method claim 1where the sensors for all members of the same team need not be uniquelyidentifiable other than uniquely distinguishing between the two teams.15. The method in claim 1 where the sport or application other thansoccer needs substantially similar relative physical locationdetermination.
 16. The method in claim 1 where the distance betweensensors are measured using electromagnetic signals.